Local ambiguity in macro definition

1d767c1
Opened by Jonas Schievink at 2019-02-18 00:05:53
macro_rules! m {
    () => ();;
}

<anon>:2:14: 2:15 error: local ambiguity: multiple parsing options: built-in NTs tt ('lhs') or 1 other options.
<anon>:2     () => ();;
                      ^

(the equivalent of $( $lhs:tt => $rhs:tt );+ $(;)* is used to parse macros)

This leaks "lhs", which is an implementation detail, and is a bad error message.

  1. Still repros.

    Brian Anderson at 2017-06-01 16:48:35

  2. Bad error message.

    Brian Anderson at 2017-06-01 16:50:30

  3. Seems to me to be primarily a bad error message -- it's not clear we should accept trailing ; (we don't accept trailing separators in any other context?)

    Niko Matsakis at 2017-06-01 16:50:47

  4. Triage: still happens:

    error: local ambiguity: multiple parsing options: built-in NTs tt ('lhs') or 1 other option.
 --> src/lib.rs:2:14
  |
2 |     () => ();;
  |              ^

error: aborting due to previous error

    Esteban Kuber at 2018-10-15 21:34:59

  5. Triage: same behavior now.

    Mazdak Farrokhzad at 2019-02-18 00:05:53